Ultraviolet (UV) radiation systems are used in the purification of water and the sanitization of a variety of items. The UV radiation and any ozone produced by the UV radiation act to kill bacteria and germs.
Traditional water disinfection systems using mercury UV lamps generate radiation through gas discharge. A critical component in the operation of mercury UV lamps is the pressure of the mercury. A UV lamp is filled with a gas containing low pressure mercury vapour and argon or xenon. When the microwaves are turned on, electrons are emitted. These electrons collide with and ionize noble gas atoms in the bulb to form a plasma by a process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp. The mercury, which exists at a stable vapour pressure equilibrium point of about one part per thousand in the inside of the tube (with the noble gas pressure typically being about 0.3% of standard atmospheric pressure), is then likewise ionized, causing it to emit light in the ultraviolet (UV) region of the spectrum predominantly at wavelengths of 253.7 nm and 185 nm. The efficiency of the lamp owes much to the fact that low pressure mercury discharges emit about 65% of their total light at the 254 nm line. About 10-20% of the light emitted in UV is at the 185 nm line.
Another problem with traditional UV lamps is the high failure rate of the lamps and ballasts. The maintenance costs resulting from frequent lamp replacements is substantial. The UV output degrades over time. Additional stand-by systems are required to keep the systems running efficiently. Another problem with the existing UV systems is the lack of a mechanism to turn the systems on and off quickly. Typically traditional lamps can only be turned on and off four times a day. Frequent switching of traditional electroded lamps wears them out very quickly.